Black Hills & Northwestern 2-6-2 "Prairie" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class 7 (Locobase 13290)

Data from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University, Volume 34, p. 284. See also the Roots of Motive Power's engine history at, last accessed 25 October 2011. (Thanks to Chris Hohl for supplying the fuel capacity.) Works number was 34666 in May 1910.

Also bound for western Washington, this wood-burning logging Prairie tank was sold to Mason County Lumber Company of Bordeaux for its BH & N two years after the Western Washington Logging Company engine described in Locobase 13284. Two differences were the slightly higher weights and the use of a link motion instead of the WWLC locomotive's Walschaert outside radial valve gear. Fuel capacity for the 7 was a modest 1 cord of wood.

In 1928, the 7 was sold to the Port of Olympia as their #2 and operated on switching duty until 1955. From then on, the locomotive operated on behalf of several preservation railroads and was substantially overhauled to current FRA standards in 1999-2001 by the Mount Rainier Scenic Railroad.

Specifications by Steve Llanso of Sweat House Media
Locobase ID13290
RailroadBlack Hills & Northwestern
Number in Class1
Road Numbers7
Number Built1
Valve GearStephenson
Locomotive Length and Weight
Driver Wheelbase9'
Engine Wheelbase24'
Ratio of driving wheelbase to overall engine wheebase 0.38
Overall Wheelbase (engine & tender)24'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers66000 lbs
Engine Weight92000 lbs
Tender Light Weight
Total Engine and Tender Weight92000 lbs
Tender Water Capacity1000 gals
Tender Fuel Capacity (oil/coal)
Minimum weight of rail (calculated)37 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter44"
Boiler Pressure160 psi
Cylinders (dia x stroke)15" x 22"
Tractive Effort15300 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.31
Heating Ability
Firebox Area71.80 sq. ft
Grate Area12.80 sq. ft
Evaporative Heating Surface689 sq. ft
Superheating Surface
Combined Heating Surface689 sq. ft
Evaporative Heating Surface/Cylinder Volume153.12
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation2048
Same as above plus superheater percentage2048
Same as above but substitute firebox area for grate area11488
Power L12733
Power MT273.87

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